1. Field of the Invention
This invention applies to furnace tube wall enclosures defining the periphery of the furnace, the lower portion of the walls consisting of spiral-wound inclined tubes and the upper portion consisting of load-carrying vertical tubes which support the lower portion and, more particularly, relates to the transition from spiral to vertical circuitry. Hereinafter, "inclined tubes" will define the spiral-wound tubes in the lower furnace and "vertical tubes" the load-carrying vertical tubes in the upper portion of the furnace. The invention concept applies to subcritical or supercritical once-through steam generators having all-welded membrane furnace walls.
A major problem in the design of such units is the support system and in the tube arrangement in the transition zone from inclined to vertical tubes. The inclined tubes are sloped up to about 30 degrees from horizontal and spiral up the furnace making several turns. The inclined tubes terminate in a header below the furnace arch for transition to vertical tubes in the upper portion of the furnace. Because a near-horizontally oriented tube can usually carry only a limited amount of static load in the vertical direction, the inclined tube portion of the furnace requires an external support system to transfer load to the vertical tubes.
2. Description of the Prior Art
Relevant prior art includes Kolling, U.S. Pat. No. 3,027,882, which discloses vertical support bars connecting inclined tubes to vertical tubes in a furnace, Bagley et al, U.S. Pat. No. 3,400,689, which discloses vertical tension members connected at their lower ends to the furnace walls and supported by springs at their upper ends, and Gorzegno et al, U.S. Pat. No. 4,116,168, which discloses inclined tubes in an intermediate furnace section connected by bifurcates to upper and lower vertical tube portions of the furnace.